Torlon® polyamide-imide: A versatile precursor for carbon molecular sieve gas separation membranes

While carbon molecular sieve (CMS) membranes have shown highly competitive gas separation properties, different polymer precursors are required to fabricate CMS membranes for different separations. For example, precursors with low fractional free volume (e.g., polyamide and polybenzimidazole) are often needed to fabricate CMS membranes with attractive H₂/CO₂ selectivity, whereas CMS membranes made from more open precursors (e.g., 6FDA-based polyimides) are more suitable to separate the larger CO₂/CH₄ pair. It is highly desirable to identify a versatile precursor that can give CMS membranes attractive for a wider spectrum of gas separations by simple control of pyrolysis conditions. In this work, we show that high-temperature pyrolysis of Torlon® polyamide-imide gives new CMS membranes with ultra-high and stable H₂/CO₂ selectivity under high-temperature mixture permeation. We also found Torlon is a versatile precursor that can give CMS membranes showing attractive CO₂/CH₄ separation performance at low pyrolysis temperature. An investigation of CMS membrane pore structures suggested that Torlon's amide-imide copolymer backbone was responsible for its versatility as a CMS membrane precursor.